<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<style type="text/css">
			.baba{
				width: 500px;
				height: 500px;
				background-color: skyblue;
			}
			.son{
				width: 200px;
				padding-top: 100%;
				background-color: black;
			}
		</style>
	</head>
	<body>
		<div class="baba">
			<div class="son"></div>
		</div>
	</body>
</html>
